From Familie Fischer:
Since summer 2007 it is possible to connect the model-railway to a Macintosh/PC not only via the serial port but also via USB (without using a USB-serial-converter) and via Ethernet. The possible connection depends solely on the selected digital central unit. The version v0.5 of SimpleDigitalLocomotive supports the connection using a serial port (or in one special case via USB using an USB-serial-converter if a MacOS-X driver is installed) and the connection via Ethernet port.
This simple program can control digital model railway systems compatible to the 6050-syntax, the Intellibox-extended-syntax or the Selectrix-syntax using the serial port of an Apple Macintosh. Locomotives, function models and accessories (accessories not for the Selectrix-syntax). Apple's standard serial port was the RS.422 (8-pin) instead of the PC-world's RS.232 (9-pin). After the release of the first iMac and G3 blue/white (1999) this serial port was no longer implemented by Apple. Macs of today have only USB as their standard serial interface.
The old Digital Interface 6050 / 6051 (which is required to connect a Mrkl6021 Central Unit with a computer) has its own serial port (DIN 8-pin) and is shipped with a cable RS.232-to-Digital- Interface-6051. Our beta-tester Carsten Bansemer reported a succesfull connection via a DB9-DB25 converter to this cable to connect an old 68k-Mac using a Mac-modem-serial cable. We have tested that installation succesfully: this way is the easiest and simplest one for setting up a stable connection.
Other digital controlling devices (for example the IB classic) have built in a RS.232 modem-serial port. A connection to the Mac is then possible with a standard Mac-modem-cable.